Interlaced content should be deinterlaced before uploading. For example, 1080i60 content should be deinterlaced to 1080p30, going from 60 interlaced fields per second to 30 progressive frames per second.

Recommended audio bitrates for uploads

YouTube uses 16:9 aspect ratio players. If you're uploading a non-16:9 file, it will be processed and displayed with either black bars on the left and right (pillar boxes) or black bars at the top and bottom (letter boxes) to make a 16:9 ratio in the player.